A mobile computing device—such as a smartphone, tablet computer, or laptop computer—may include functionality for determining its location, direction, or orientation, such as a GPS receiver, compass, or gyroscope. Such a device may also include functionality for wireless communication, such as BLUETOOTH communication, near-field communication (NFC), or infrared (IR) communication or communication with a wireless local area networks (WLANs) or cellular-telephone network. Such a device may also include one or more cameras, scanners, touchscreens, microphones, or speakers. Mobile computing devices may also execute software applications, such as games, web browsers, or social-networking applications. With social-networking applications, users may connect, communicate, and share information with other users in their social networks.
A structured document such as a web page may include, for example, page layout information, scripts, page content such as text, media data (e.g., graphics, photos, video clips), and executable code objects (e.g., a game executable within a browser window or frame). Structured documents may be implemented with languages and technologies such as Hypertext Markup Language (HTML), Extensible Markup Language (XML), Extensible Hypertext Markup Language (XHTML), JavaScript, WebGL, Cascading Style Sheet (CSS) including CSS animations and transitions, and, frequently, Java. A structured document may itself include references to multiple structured documents and contents. For example, a web page may include one or more inline references by incorporating Uniform Resource Locations (URLs) and/or script code (e.g., JavaScript, PHP, AJAX) that in response to a user event (e.g., a mouse click, a mouse hover-over), causes an application displaying the web page in a graphical user interface to dynamically retrieve content specified by an URL and the script code.